Three-phase AC (Alternating Current) motors have been widely used, an example of which is disclosed in Japanese Patent Application Publication No. 2005-110431.
FIG. 120 is an axial cross sectional view illustrating a schematic structure of a surface permanent magnet synchronous motor as an example of such three-phase AC motors.
The motor illustrated in FIG. 120 is provided with an output shaft 811, a substantially annular rotor core 812, and a pair of N and S poles 817 and 818 of permanent magnets. The motor is also provided with a pair of bearings 813, a substantially annular stator core 814, and a substantially cylindrical inner hollow motor housing 816 with an opening in its axial direction.
The output shaft 811 is fixedly mounted on an inner circumference of the rotor core 812. The output shaft 811 is disposed in the opening of the motor housing 816 such that both ends thereof project from the opening, and the rotor core 812 is installed in the motor housing 816. The output shaft 811 is rotatably supported by the motor housing 816 with the bearings 813. The N and S poles 817 and 818 are, for example, mounted on the outer circumference of the rotor core 812 such that the N and S poles are alternatively arranged in the circumferential direction of the rotor core 812. The rotor core 812 and the N and S poles 817 and 818 of the permanent magnet constitute a rotor of the motor.
The stator core 814 is made up of a plurality of magnetic steel sheets stacked in alignment. The stator core 814 is installed in the motor housing 816 such that its inner circumference is opposite to the outer circumference of the rotor core 812 with an air gap therebetween. Three-phase stator windings are installed in the stator core 814. Ends 815 of the three-phase stator windings are drawn out from the stator core 814. The three-phase stator coils and the stator core constitute a stator.
FIG. 121 is a lateral cross sectional view taken on line AA-AA in FIG. 120. In these FIGS. 120 and 121, a two-pole, 12-slot three-phase permanent magnet synchronous motor is used. In order to simply illustrate the structure of the motor, the hatching of the output shaft 811 is omitted in illustration in FIG. 121.
As each of three-phase stator windings of the synchronous motor illustrated in FIGS. 120 and 121, a distributed, full pitch winding is used. In FIG. 121, the stator core 184 consists of an annular back yoke and 12 teeth 821, 822, 823, 824, 825, 826, 827, 828, 829, 82A, 82B, and 82C projecting inwardly and circumferentially arranged at equal pitches therebetween. Spaces between circumferentially adjacent teeth provide 12 slots of the stator core 814. U-, V-, and W-phase stator windings are distributedly arranged in corresponding slots of the stator core 184.
Specifically, a first U-phase winding is wound from a slot 82Q to a slot 82K, and a second U-phase winding is wound from a slot 82D to a slot 82J. A first V-phase winding is wound from a slot 82G to a slot 82P, and a second V-phase winding is wound from a slot 82H to a slot 82N. A first W-phase winding is wound from a slot 82L to a slot 82F, and a second W-phase winding is wound from a slot 82M to a slot 82E. The pitch between the slots in which each of the U-, V-, and W-phase windings is wound is set to 180 electrical degrees.
FIG. 122 is a developed view of the inner periphery of the stator core 184 in its circumferential (rotational) direction; the horizontal axis of the view represents positions of the stator in its rotational direction by corresponding electric angles in degrees. Note that, because the motor is a two-pole motor, an electric angle of a given position of the stator in its rotational direction is in agreement with a mechanical angle of the corresponding position of the stator.
In FIG. 122, reference character U represents a terminal of the second U-phase winding, and, to the terminal U, a U-phase current Iu is supplied. Reference character V represents a terminal of the second V-phase winding, and, to the terminal V, a V-phase current Iv is supplied. Reference character W represents a terminal of the second W-phase winding, and, to the terminal W, a W-phase current Iw is supplied.
Reference character 831 represents a connection wire that connects the first and second U-phase windings in series, reference character 832 represents a connection wire that connects the first and second V-phase windings in series, and reference character 833 represents a connection wire that connects the first and second W-phase windings in series. The U-phase coil (series-connected U-phase windings), V-phase coil (series-connected V-phase windings), and W-phase coil (series-connected W-phase windings) are connected to each other in star configuration to provide a stator coil of the stator. Reference character N represents a neutral point of the star-connected three-phase coils.
FIG. 123 schematically illustrates the connecting structure of the stator coil (three-phase coils) of the permanent magnet synchronous motor set forth above and a control device for the permanent magnet synchronous motor. In FIG. 123, reference character 834 represents the U-phase coil, reference character 835 represents the V-phase coil, and reference character 836 represents the W-phase coil.
The control device is provided with a three-phase inverter and a DC battery 84D. The three-phase inverter consists of a first pair of series-connected high- and low-side power transistors 841 and 842, and a second pair of series-connected high- and low-side power transistors 843 and 844, and a third pair of power transistors 845 and 846. Flywheel diodes 847, 848, 849, 84A, 84B, and 84C are connected in antiparallel across the power transistors 841, 842, 843, 844, 845 and 846, respectively.
The three-phase inverter is operative to convert a DC voltage supplied from the DC battery 84D into three-phase AC currents Iu, Iv, and Iw, and to supply the three-phase AC currents Iu, Iv, and Iw to the three-phase coils 834, 835, and 836, respectively, thus driving the three-phase motor.
Such surface permanent magnet synchronous motors illustrated in FIGS. 120 to 123 have been widely utilized as high-efficient motors. However, from higher performance, smaller size, and lower cost standpoints, there have been problems in these surface permanent magnet motors depending on their applications.
Specifically, assuming that a current I is supplied to one of the stator windings of such a permanent magnet synchronous motor and a magnet flux density B applied to a permanent magnet rotor of the motor, a force F acts on the rotor as basic characteristics of the brushless motor in accordance with the following equation:F=BIL 
where L represents the length of an effective portion of each stator winding.
Thus, a torque T generated by the brushless motor is represented by the following equation:T=FR 
where R represents the radius of the rotor.
FIG. 124 schematically illustrates an example of three-phase AC motors with a two-pole multi-flux-barrier rotor. The structure of a stator of the three-phase AC motor illustrated in FIG. 124 is identical to that of the permanent magnet synchronous motor illustrated in FIG. 121.
The rotor of the three-phase AC motor consists of a soft magnetic material rotor core. The rotor also consists of a plurality of slits 852 formed in the rotor core so as to be arranged at intervals therebetween in parallel to one diameter of the rotor core.
The rotor further consists of a plurality of thin magnetic paths 851 each formed between a corresponding one of the slits 852 and a corresponding alternative one of the slits 852 adjacent thereto. Specifically, the slits 852 are operative to barrier flux in the rotor core. Thus, the slits 852 are referred to as “flux barriers”.
The flux barriers 852 restrict the direction in which the flux passes in the direction of each slit (for example, the vertical direction in FIG. 124). One ant the other sides of the rotor core in the direction of each slit serve as a pair of magnetic poles of the rotor.
Note that an identical type of the control device illustrated in FIG. 123 can be used to drive these three-phase AC motors with such a multi-flux-barrier.
A lateral cross section of another conventional motor is illustrated in FIG. 125. The motor illustrated in FIG. 125 is called “switched reluctance motor”. An example of such switched reluctance motors is disclosed in Japanese Patent Application Publication No. 2002-272071.
The switched reluctance motor consists of a substantially annular rotor 86L made up of a plurality of magnetic steel sheets stacked in alignment. The rotor 86L has, at its outer circumferential surface, four salient poles. The four salient poles are circumferentially arranged at regular pitches. The switched reluctance motor also consists of a substantially annular stator with equal-pitched six teeth. There have been many studies of such switched reluctance motors, but a few switched reluctance motors have been put to practical use.
Reference numeral 861 represents a tooth around which an A-phase coil is concentrically wound in positive and negative directions (see reference numerals 867 and 868); this causes the tooth 861 to serve as an A-phase stator pole. The positive direction represents a direction into the paper of FIG. 125, and the negative direction represents a direction out of the paper of FIG. 125.
Reference numeral 864 represents a tooth. As illustrated by a broken line, an A-phase coil is concentrically wound around the tooth 864 in the positive and negative directions (see reference numerals 86E and 86D); this causes the tooth 864 to serve as a negative A-phase stator pole. The A-phase coils are connected to each other in series through a connection wire to provide an A-phase winding.
A group of conductors (wires) in each A-phase coil through each of which a current in the positive direction flows is defined as “a positive A-phase winding”, and a group of conductors (wires) in each A-phase coil through each of which a current in the negative direction flows is defined as “a negative A-phase winding”. That is, reference numerals 867 and 86E represents positive A-phase windings, and reference numerals 868 and 86D represent negative A-phase windings.
When the rotor 861, is presently located at an rotational angle θr relative to a reference position R illustrated in FIG. 125, an A-phase current is supplied to flow through each of the positive A-phase windings 867 and 86E in the positive direction, and flow through each of the negative A-phase windings 868 and 86D in the negative direction. This generates a magnetic flux illustrated by an arrow 86M in FIG. 125
The magnetic flux 86M causes a magnetic attractive force between the A-phase stator pole 861 and one salient pole of the rotor 86L close thereto and between the A-phase stator pole 864 and one salient pole of the rotor 86L close thereto. The attractive force creates a torque to rotate the rotor 86M in counterclockwise direction.
Reference numeral 863 represents a tooth around which a B-phase coil is concentrically wound in the positive and negative directions (see reference numerals 86B and 86C); this causes the tooth 863 to serve as a B-phase stator pole. Reference numeral 866 represents a tooth. As illustrated by a broken line, a B-phase coil is concentrically wound around the tooth 866 in the positive and negative directions (see reference numerals 86J and 86H); this causes the tooth 866 to serve as a negative B-phase stator pole. The B-phase coils are connected to each other in series through a connection wire to provide a B-phase coil member.
Like the A-phase winding, a group of conductors in each B-phase coil through each of which a current in the positive direction flows is defined as “a positive B-phase winding”, and a group of conductors in each B-phase coil through each of which a current in the negative direction flows is defined as “a negative B-phase winding”. That is, reference numerals 86B and 86J represents positive B-phase windings, and reference numerals 86C and 86H represent negative B-phase windings.
Reference numeral 865 represents a tooth around which a C-phase coil is concentrically wound in the positive and negative directions (see reference numerals 86G and 86F); this causes the tooth 865 to serve as a C-phase stator pole. Reference numeral 862 represents a tooth. As illustrated by a broken line, a C-phase coil is concentrically wound around the tooth 862 in the positive and negative directions (see reference numerals 869 and 86A); this causes the tooth 862 to serve as a negative C-phase stator pole. The C-phase coils are connected to each other in series through a connection wire to provide a C-phase coil member.
Like the A- and B-phase windings, a group of conductors in each C-phase coil through each of which a current in the positive direction flows is defined as “a positive C-phase winding”, and a group of C-phase windings in each C-phase coil through each of which a current in the negative direction flows is defined as “a negative C-phase winding”. That is, reference numerals 86G and 869 represents positive C-phase windings, and reference numerals 86F and 86A represent negative C-phase windings.
In the motor illustrated in FIG. 125, the A-phase current, a B-phase current, and a C-phase current are sequentially supplied to the corresponding A-phase, B-phase, and C-phase coils, respectively, according to the rotational position of the rotor 86L relative to the reference position. This creates a continuous torque as a total torque to rotate the rotor 86L.
Simultaneously reversing the direction of the A-phase current flowing through each of the positive A-phase windings and that of the A-phase current flowing through each of the negative A-phase winding maintains unchanged the direction of the created torque because the magnetic attractive force of the soft magnetic material creates the torque. This is established in the B-phase and C-phase currents as well. However, in order to lower the number of alternating rotor poles, the directions of the A-, B-, and C-phase current flows illustrated in FIG. 125 are known to thereby reduce iron loss in the rotor.
The switched reluctance motor illustrated in FIG. 125 has the following features:
The first feature is that the switched reluctance motor is low in cost because it uses no permanent magnets.
The second feature is that, because each of the stator windings is concentratedly wound around a corresponding tooth, the arrangement of individual stator windings is simple.
The third feature is to utilize torque based on high flux density because the magnetic flux acting between the salient poles of the stator and those of the rotor is based on a saturation flux density of the magnetic steel sheets.
The fourth feature is that the rotor can be rotated at a higher RPM because the rotor is rugged.